Question

Fluoridation of drinking water is employed in many places to aid in the prevention of tooth decay. Typically the F^– ion concentration is adjusted to about 1 ppb. Some water supplies are also “hard”; that is, they contain certain cations such as Ca^{2 +} that interfere with the action of soap. Consider a case where the concentration of Ca^{2 +} is 8 ppb. Could a precipitate of CaF₂ form under these conditions? (Make any necessary approximations.)